What is the equation for calculating the mass number of an isotope?

The mass number of an isotope is calculated by adding the number of protons and neutrons in the nucleus of the atom. The equation is:

Mass Number = Number of Protons + Number of Neutrons

It's important to note that the number of protons is also known as the atomic number, and it's unique for each element. The number of neutrons can vary, which is what creates different isotopes of the same element.